In recent years, demand for natural colourants has been steadily increasing in the food and beverage industry due to consumers' concerns about synthetic colourants. Anthocyanins are natural compounds that are synthesised in plants and can offer a wide range of colours. Anthocyanins are among the most preferred natural colourants because they function not only as natural colourants and but have antioxidant properties, and have been shown in many studies to have health-promoting effects.
Anthocyanins are the most significant flavonoid pigments. They are based on a core 15-carbon (C15) structure of two aromatic rings (the A and B rings) joined by a third ring of three carbons and one oxygen (the C-ring) (Andersen and Jordheim 2006). The anthocyanin is formed by glycosylation of a core anthocyanidin structure—in the great majority of cases the initial O-glycosylation is at the C-3 position. Additional modification by hydroxylation, acylation, methylation and further glycosylation generates the large number of known anthocyanin variant structures. Although over 30 different core anthocyanidins have been identified, the six common ones (pelargonidin, cyanidin, peonidin, petunidin, malvidin) are the basis of about 90% of the known anthocyanins. Some of the less common anthocyanidins contribute important flower pigments in a small number of species, such as the 3-deoxyanthocyanins and 6- and 8-hydroxyanthocyanins.
However, the low stability of anthocyanins during and after extraction from plants and when added to food or beverage products is a major hurdle for commercially utilizing anthocyanins as colourants. In plants, anthocyanins are a subclass of flavonoids that are widely present in many species. Anthocyanins are synthesised in a branch of the flavonoid biosynthesis pathway. Upon biosynthesis, anthocyanins are usually transported into and stored in the central vacuole of the plant cell. Under the vacuolar conditions, anthocyanins are usually positively charged and present in coloured forms. In the vacuole, anthocyanins accumulate in a soluble form and/or as anthocyanic vacuolar inclusions (AVIs) (Markham et al. 2000).
In comparison with completely soluble anthocyanins, AVIs can be highly stable under wide range of conditions (unpublished data). Some of these conditions are compatible with food and beverage products. Therefore, use of AVIs in food and beverage products could be an effective way to utilise anthocyanins as natural colourants in such products.
However, extraction of AVIs from plants in sufficient quantities for use in food, beverage and other products, may be limited by the efficiency of purification procedures and quantity of the appropriate AVI-containing plant material available.
It would therefore be beneficial to develop methods for stabilising anthocyanins in a form similar to AVI from more readily available/or more easily purifiable components.
It is therefore an object of the invention to provide a method for producing AVI-like structures in vitro.